I report the bug that I cannot use nvidia-settings to change twinview after disconnect a LCD at vga and connect another at displayport here:http://www.nvnews.net/vbulletin/showthread.php?t=155651
After readinghttp://www.nvnews.net/vbulletin/showthread.php?t=123781
it seems when the old display is no longer connected, I cannot remove metamodes associated to it. I think this could be handled automatically in nvidia drivers: remove all the dynamic metamodes associated to a display before remove the display, or simply clear all the dynamic metamodes whenever the display configuration is changed. Then at least the users will have the chance to use nvidia-settings to setup the system again instead of restart X.